The present disclosure relates to a transmission/reception module. FIG. 2 of Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2005-535245 discloses a multimode wireless module that can handle different communication standards and frequency bands. The global system for mobile communications (GSM) (registered trademark), personal digital cellular (PCS), and digital cellular system (DCS) standards are used as the different communication standards. In a PCS signal transmission system of the multimode wireless module, a PCS signal output from a power amplifier is transmitted from an antenna after passing through a high pass filter. The high pass filter allows a PCS signal and a DCS signal to pass therethrough, but blocks a GSM signal. In a PCS signal reception system of the multimode wireless module, a DCS signal, between a PCS signal and a DCS signal, that has passed through the antenna and the high pass filter is blocked by a band pass filter. A PCS signal that has passed through the band pass filter is amplified by a low-noise amplifier. A phase-shift circuit, which is formed of a series capacitor element and a shunt inductor element, is provided between the high pass filter and the band pass filter with ¼ wavelength transmission lines interposed therebetween. The values of the series capacitor element and the shunt inductor element of the phase-shift circuit are selected such that the impedances of the ¼ wavelength transmission lines match the input impedance of the band pass filter. A DCS signal transmission system and a DCS signal reception signal system have the same configurations as the PCS signal transmission system and the PCS signal reception system, respectively.
However, a signal component of part of a transmission signal output from the power amplifier of the PCS/DCS signal transmission system may pass through the high pass filter and the band pass filter without necessarily being sufficiently attenuated and may be input to the low-noise amplifier of the PCS/DCS signal reception systems. Depending on the impedance at the input node of the low-noise amplifier with respect to the transmission signal, the gain of the transmission signal may exceed the gain of a reception signal, and there is a fear that the isolation characteristics of the module will be degraded.